Predictors of driving cessation in mild-to-moderate dementia

Although physicians in most provinces are mandated to report patients whose driving ability is impaired by illness, little is known about dementia-related factors associated with driving cessation. The purpose of our study was to explore factors that may affect the likelihood of driving cessation in a sample of elderly, community-dwelling patients with dementia.

A 3-year prospective study, the Canadian Outcomes Study in Dementia (COSID) has enrolled 883 patients with mild-to-moderate dementia at 32 centres across Canada. Assessment tools included the Mini-Mental State Examination (MMSE) for cognition, the Global Deterioration Scale (GDS) for staging (severity), the Functional Autonomy Measurement System (SMAF) for function, and the Neuropsychiatric Inventory (NPI) for behaviour. Factors associated with the decision to quit driving after the baseline assessment were tested with Cox survival analysis.

Of 719 subjects who were or had been drivers, 203 (28.2%) were still driving at baseline. Over an observation period that averaged 23 months, 97 (48.5%) of 200 patients quit driving. Factors predictive of driving cessation included GDS (hazard ratio [HR] 1.68, 95% confidence interval [CI] 1.15-2.45), MMSE score (HR 0.90, 95% CI 0.83-0.97) and NPI findings (HR 1.63 for presence of > or = 3 behaviours, 95% CI 1.01-2.62). Among the NPI behaviours, when they were analyzed separately, agitation led to a decreased likelihood of driving cessation (p = 0.019), whereas apathy (p = 0.031) and hallucinations (p = 0.050) led to an increased likelihood.

Cognitive impairment and behaviours such as agitation, apathy and hallucinations were significant predictors of driving cessation in patients with a mild to moderate degree of dementia. These findings should be considered when one counsels patients and their families.